FROM READERS: Professor discusses pros and cons of Paleo diet for athletes

Friday, March 15, 2013 | 6:00 a.m. CDT

BY
PAM HINTON/MISSOURIAN READER

Pam Hinton is an associate professor of nutrition and exercise physiology at MU. She is also a contributor to the Columbia cycling blog ComoCyco.com. This is one of her posts, which published March 5.

Hi Pro Pam,

A fellow racer told me the Paleo diet is the secret for progressing as an endurance athlete. This seems completely backwards to me; I’ve been participating in endurance sports my entire life and have always been advised to eat a carbohydrate-rich diet.

Would you please explain how an endurance athlete may benefit from a fat and protein rich diet?

Thanks!Richard Tête

Hi, Richard. Thanks for the question.

First, let’s take a look at the Paleo diet and the rationale behind it. This diet, which is also referred to as the Caveman, Stone Age, or Warrior diet, is based on the premise that the ideal diet is that which was consumed by our ancestors 10,000 years ago — prior to the agricultural revolution.

The assumption is that humans are “genetically programmed” to eat the foods that were consumed by our hunter-gatherer ancestors and that the chronic diseases (obesity, diabetes, high blood pressure, heart disease) that afflict Western societies can be attributed to consumption of agricultural products.

Of course, refined or processed foods are also off limits. As evidence that “cavemen” were healthier than today’s American, proponents of the Paleo diet cite modern day non-Western hunter-gatherer populations who are “fitter” and do not suffer from high cholesterol or hypertension.

As you might expect, there is some controversy surrounding the Paleo diet. The key assumptions on which the Paleo diet is based have been questioned. First, were our Stone Age predecessors really healthy? Some critics of the Paleo diet say “no.” Their life expectancy was much shorter, and they died of injury, infectious disease, or malnutrition (insufficient energy, protein, vitamins/minerals).

Because of advancements in medicine and nutrition, malnutrition and related diseases are relatively rare; today humans suffer from diseases caused by nutrient excess. In addition, critics argue that, if it is optimal to replicate the environmental conditions of 10,000 years ago because we are “genetically well adapted” to them, then we should not stop with diet, but should extend the “caveman” lifestyle to our living conditions, use of antibiotics, etc.

The argument that the foods humans “encountered in our original and natural ecological niche” are optimal assumes that human evolution ceased 10,000 years ago. There is evidence, however, that the human gastrointestinal tract is highly adaptable and continually evolving.

Other critics point to the inconsistencies of the Paleo diet. For example, the Paleo diet for athletes recommends protein powder (including dairy-based whey protein), prepared baby food, liquid meal replacements (e.g., Ensure), sports bars, as well as supplementation with vitamins C, E, and D. Obviously, none of these were available to cavemen! Likewise, the fruits, vegetables, meat, and fish available to the consumer today are vastly different from the native plants and wild game that were available to our Paleolithic ancestors.

In addition to these issues, there is the question of whether the Paleo diet is “healthful” or “performance-enhancing,” regardless of the rationale behind the diet. First, let’s consider the health effects of the Paleo diet. Of course, the consequences of a dietary change depend on an individual’s diet when he or she decides to make a change.

For most Americans, eating more fruits and vegetables, as well as lean meat and fish, and reducing consumption of processed foods will lower overall energy intake (resulting in weight loss) and will increase intake of vitamins, minerals, and “good” fats (omega-3s) that are often low in a typical U.S. diet. These dietary changes will favorably affect health by reducing risk of obesity, diabetes, heart disease, high blood pressure, and cancer.

However, there is considerable concern about a diet devoid of dairy products. Without dairy products it is impossible to consume enough calcium and vitamin D without taking supplements. Although proponents of the Paleo diet argue that the diet reduces calcium needs, supplemental calcium and vitamin D are needed to prevent loss of bone mineral to maintain blood calcium levels.

So, finally, how might the Paleo diet affect your performance? Is it “the secret” that will allow you to progress to the next level as an endurance athlete? Some aspects of the Paleo diet might be helpful, but others might actually hurt your performance.

Let’s start with the potential downsides first. There are multiple reasons why, as an endurance athlete, you have been advised to eat a carbohydrate-rich diet. First, you need a lot of carbohydrates to replenish your liver and muscle glycogen stores, which serve as the primary source of glucose for moderate- and high-intensity training. Without glycogen available, you will feel fatigued, sluggish and will be unable to train at high intensity.

Second, carbohydrate ingestion prevents the post-exercise increase in cortisol, the stress hormone that has immuno-suppressive effects and that is linked to upper respiratory infections and overtraining syndrome. Third, your nervous system (including your brain) and red blood cells use glucose for energy. Because fruits and vegetables are the primary source of carbohydrates on the Paleo diet, this diet tends to be low in carbohydrates (<35% of total kilocalories).

It is nearly impossible to consume the recommended 6-10 grams of carbs per kilogram of body weight (1680–2800 kcal of carbs for a 70-kg athlete) eating only fruits and vegetables! With very low carb intake and constantly depleted glycogen stores, your liver will make glucose from protein to fuel your brain and red blood cells. The protein used in the process comes from your organs, including your heart and skeletal muscle — obviously not ideal for an athlete.

So while the Paleo diet facilitates weight loss — initially due to glycogen depletion (~3-5 pounds) and then loss of lean body mass — this weight loss does not necessarily equate to beneficial changes in body composition.

In addition to the argument that grains and legumes were not available to cavemen, the Paleo diet argues that these foods are “bad” because they cause a rapid rise in blood glucose and, therefore, in insulin (i.e., have a high glycemic index). The Paleo diet also makes the case that a grain-based diet leaves an athlete “starved for protein and trace nutrients.”

However, not all grains are created equal. Unrefined cereal grains (e.g., long-grain rice, oats, whole-grain baked goods) have a moderate glycemic index and are a good source of B vitamins and soluble fiber. Likewise, legumes are an excellent source of protein, B vitamins, and fiber, and soy is associated with reduced risk of heart disease and osteoporosis. In addition, consumption of grains and legumes does not preclude eating fruits and vegetables or lean meat or fish.

Which brings us to the potential benefits of some of the Paleo diet recommendations. Consumption of adequate high-quality protein is important for recovery from training — in particular, recovery following high-intensity and/or long-duration exercise, which causes greater muscle breakdown. In addition to providing amino acids, meat is an excellent source of iron and zinc.

Endurance athletes need 1.6–1.7 grams of protein per kg of body weight per day (~400–500 kcal protein for a 70-kg athlete). The branched-chain amino acids (BCAAs) have received considerable attention recently; in particular, the BCAA leucine (5–10 grams) has been shown to stimulate protein synthesis, especially when combined with exercise. (Unfortunately, the Paleo diet prohibits milk, which is an excellent source of BCAAs, because of milk’s high BCAA content and easily digested whey protein.) Another potential benefit of the Paleo diet is increased consumption of omega-3 fatty acids via fish. The omega-3s in fish (EPA and DHA) have multiple health benefits, including anti-inflammatory effects.

The bottom line is that endurance athletes need a lot of dietary carbohydrate to fuel high-intensity training and replenish their glycogen stores. So, you should not discard the advice to consume a high-carbohydrate diet. You might, however, benefit from ensuring the source of carbs in your diet — include fresh fruits and vegetables, unrefined whole grains, and legumes.

Likewise, endurance athletes also need high-quality protein, preferably from unprocessed lean meat, which also provides iron and zinc, and from dairy products, which are the major contributors of calcium and vitamin D. The good news is that you do not have to choose between the “conventional” high-carb diet and the Paleo diet: you can have the best of both.

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